1. Field of the Invention
This invention relates to an electronic clinical thermometer for displaying the life of a battery by using part of the seven-segment digits on a digital display device.
2. Description of the Related Art
In recent years, instead of clinical thermometers made of glass containing mercury, electronic clinical thermometers have spread. The electronic clinical thermometer measures the body temperature by use of its temperature sensor and integrated circuit and displays the body temperature by the digital display device having display patterns of seven-segment digits.
The electronic clinical thermometer operates on a small bettery as a power source. When the voltage of the battery is reduced below a predetermined value, the operation of the temperature measuring circuit becomes unstable, which leads to errors in measurement. Accordingly, a battery voltage detecting circuit is provided for detecting the voltage drop of the battery, and corresponding to a detecting signal of the battery voltage detecting circuit, a battery life warning display is provided so as to assure the reliability of the electronic clinical thermometer.
Now, the basic arrangement of the electronic clinical thermometer and some examples of conventional battery life warning displays will be explained.
FIG. 1 is a block diagram showing the basic arrangement of an electronic clinical thermometer with a battery life warning display. This basic arrangement has been used conventionally and also is used in the present invention. 101 is a reference oscillation circuit for oscillating a reference signal f.sub.o which does not vary with time and for sending the reference signal f.sub.o to a control signal generating part 103. The control signal generating part 103 receives the reference signal f.sub.o and sends a variety of control signals such as a gate signal .phi..sub.g, a latch signal .phi..sub.B and a sampling signal .phi..sub.s. 102 is a temperature oscillation circuit. This temperature oscillation circuit 102 incorporates a temperature detecting sensor and oscillates a temperature sensor signal f.sub.t whose frequency varies with the body temperature. 104 is a control part which is on or off in response to the gate signal .phi..sub.g of the control signal generating part 103 and sends the temperature sensor signal f.sub.t, which has applied while the control part 104 is on, as a temperature measuring signal .phi..sub.A. 120 is a body temperature measuring circuit comprising a counter part 105, a memory part 106 and a decoder part 109. The temperature measuring circuit 120 works as follows: The counter part 105 counts the temperature measuring signal .phi..sub.A and sends a temperature information signal D.sub.t to the memory part 106. The memory part 106, in turn, compares the temperature information signal D.sub.t which has newly been applied from the counter part 105 with a maximum temperature information signal D.sub.m which has already been stored in the memory part 106 corresponding to the latch signal .phi..sub.B, and the memory part 106 stores the higher temperature information as the maximum temperature information signal D.sub.m, thus continuing to update the information on the maximum temperature which rises with the lapse of time during the temperature measurement. The maximum temperature information signal D.sub.m which varies momentarily as above is decoded into a display signal D.sub.d of seven segments by the decoder part 109 and displayed numerically in seven-segment patterns on a digital display part 110. On the other hand, 107 is a battery voltage detecting circuit. A detection level is predetermined by an external resistance 108. When the battery voltage detecting circuit 107 detects the fact that the battery voltage is reduced below the predetermined detection level, it produces a battery life warning signal .phi..sub.C and applies it to the decoder part 109 of the temperature measuring circuit 120. As a result, the decoder part 109 produces a warning display signal D.sub.d for indicating a battery life warning mark on the digital display part 110.
FIG. 2 is a plan view of a conventional digital display device 110 with a battery life warning mark, in which 110A denotes a ten degree (10.degree.) digit of the measured temperature value; 110B denotes a one degree (1.degree.) digit; 110C denotes a decimal point; 110D denotes a point one degree (0.1.degree.) digit; 110E denotes a unit; and 110F is a display pattern showing a battery life warning mark. The digital patterns 110A, 110B and 110D comprise well known seven-segment patterns, and the battery life warning mark 110F has a small pattern of the shape of a battery. Usually, the maximum temperature information corresponding to the display signal D.sub.d applied by the body temperature measuring circuit 120 is displayed on the seven-segment patterns of the digital display device 110, and the battery life warning mark 110F is not lit. However, when the battery voltage is reduced below the detection level and thus the battery life approaches an end, the battery life warning signal .phi..sub.C is produced and the battery life warning mark 110F is lit to urge the user to replace the battery.
Now, the operation of the battery life warning of the electronic clinical thermometer has been discussed.
To take other conventional examples of the battery life warning displays each provided on the display part of the electronic digital clinical thermometer, as disclosed in U.S. Pat. Re. 29,637, there is an alphabetic pattern of "BAT" which reminds the user of its battery and as disclosed in U.S. Pat. No. 4,074,515, there is a seven-segment pattern display which changes the color.
Still, the object of the battery life warning display is to notify the user of the necessity for the replacement of the battery. It means that unless the battery is replaced, the correct measurement could not be made any more. Therefore, the result of the battery voltage detection is the highly important information. Nevertheless, in view of the shape of the typical electronic thermometer, the digital display device 110 is limited to about 20 mm in overall length and about 6 mm in width. On such small display surface area, there are provided some display patterns such as a plurality of seven-segment patterns, a decimal point and a unit mark, and therefore the battery life warning mark provided on the limited space should become a very small shape. Thus the conventional mark fails to perform the function of warning.
Also, as in U.S. Pat. No. 4,074,515, a battery life warning display which changes the color of the seven-segment patterns can perform the proper function of warning because of its large-sized segment patterns. However, since the color changing digital display must be used, the cost is raised and such display cannot be used for low-cost electronic thermometers.